Since the dawn of civilization, humans have had a ceaseless fascination with light. Light, in a sense, is now the mechanism with which humans continuously attempt to cast the unknown into the shadows. Whether it be gathering around a campfire, sleeping with a night light, or filling streets with neon advertisements, light is omnipresent in today’s society. Sure, some light is necessary to allow people to see where they are going in the dark, but more often than not, humans use light to placate a fear of the unknown. It turns out that this fear is somewhat justified, at least from an evolutionary standpoint. Thousands of years ago, when larger predators relentlessly pursued early humans, the act of gathering around a fire during the night helped humans to survive. The light provided by the fire allowed early humans to spot predators and scare them away, and it helped them feel more secure until morning finally arrived.

Historical and predicted spread of light pollution in the United States.

Many scientists believe that a fear of the dark stems from similar events in early human history. Since then, creation and manipulation of light has shaped the course of modern history, and as time has progressed, light has become an inseparable component of society. Most of society has no idea, though, that there is a “dark side” of light usage, known as light pollution, which will soon affect every corner of the world.

Light pollution is generally defined as the overuse or misuse of artificial lighting. In other words, when too much light is used or is directed wastefully up into the sky, light scatters off particles in the atmosphere, creating a glow of excess light. Since artificial light is most intense and excessive in urban areas, cities tend to have the worst light pollution. It is one of the most pervasive types of pollution and has a stunningly long list of consequences, affecting human life along with the entirety of the biosphere. Such consequences include:

Reduced or little night sky visibility

Possible link to increased air pollution in cities

Disruption of biological processes in nature

Disruption of sleep cycles

Waste of energy and money

The effects of air and light pollution on night sky visibility.

The most noticeable consequence of light pollution is its effect on night sky visibility. One hundred years ago, the majority of the world could look up at the night sky and see hundreds of thousands of stars scattered across the backdrop of a crisp black sky and the Milky Way. Now, inner city dwellers may only be able to see a few bright stars. Even worse, light pollution from cities can spread out and affect areas miles away. Today, scientists estimate that nearly every part of the continental United States is, in some way, affected by light pollution. This understandably presents a huge problem for astronomers and physicists who need clear views of the sky to do research, so their instruments have to be built in increasingly remote locations. In the near future, when light pollution even creeps into isolated corners of the world, a faint glow will shroud the sky and block out some of the true wonders of the universe.

NASA observatories are also affected by light pollution, both on Earth and in space. NASA’s Earth Observatory System regularly captures breathtaking views of the Earth at night, dotted with city lights and even some large wildfires. Today, though, it is impossible for NASA to get a good view of the Earth as it once was: completely dark. Surprisingly, the lights visible in such images reveal some distinct geophysical and political borders, notably the divide between North and South Korea and the beginning of the Himalayas. Even some large groups of lit fishing boats are visible on the Nile River. Through these observations, though the intensity of light pollution becomes overwhelmingly clear, NASA has managed to observe the spread of artificial lighting with unprecedented detail and learn a great deal more about human impact on the world.

Bright city lights have been linked to an increase in air pollution.

All too often, some of that human impact comes in the form of pollution, and one of the most astounding consequences of light pollution is its possible effect on air pollution in cities. Smog obviously does not help light pollution; in fact, it essentially amplifies it, because the light is scattered more and trapped by the pollutants in the air. No one ever thought, though, that light pollution might make air pollution worse. According to a study by the National Oceanic and Atmospheric Association and the Cooperative Institute for Research in Environmental Sciences, light pollution seems to interfere with natural chemical processes that clean the air at night. Their findings, presented at the American Geophysical Union in 2010, indicate that nitrate radicals, which are destroyed by sunlight during the day, can also be inactivated by light pollution. This causes the breakdown of pollutants to slow by up to 7 percent and can increase pollutant levels the next day by up to 5 percent. While that may not seem significant, over time, that adds up to a very large amount of unnecessary pollution. In fact, by directing light only where it is needed using efficient outdoor lighting fixture design, much of this can easily be avoided.

In nature, natural light and dark patterns are essential for the reproduction and survival of many species. Frogs, for example, refrain from singing their mating songs in the presence of too much artificial light, and migrating birds can become easily confused by city lights, often fatally crashing into skyscrapers. Thousands of birds die each year from this disorientation. Turtles, which use the reflection of the moon on ocean water to find their way back to the sea after hatching, can become disoriented by light pollution from brightly lit beachfront developments. These are just a handful of the affects that light pollution has on animals, and the consequences of such changes on their environments could be astonishing.

Humans are not immune to the consequences of light usage. Light pollution affects humans psychologically, physically, and even economically. Every living creature on Earth has evolved with the natural cycle of day and night. Now, people are altering that cycle with light pollution, so physical and mental reactions to the change should come as no surprise. Excessive time in brightly lit areas can trigger a myriad of sleep disorders, some of which are linked to depression. Some studies even claim to have evidence that links increased cancer risks to light pollution, though there is lack of sufficient evidence to say for sure either way. Since light pollution is caused by using too much light or shining light where it is not needed, it corresponds with a huge amount of wasted money and energy leading to many other types of pollution.

Outdoor lighting design efficiency.

Light pollution is clearly a significant problem, and while there is no way to completely stop light pollution, it is fairly simple to control. By installing efficient outdoor lighting fixtures that direct light down and out at the appropriate angle needed, light pollution can be reduced significantly. In fact, this would probably save money long-term, too, because lights would be tremendously more energy-efficient and prevent other types of pollution. Using less light, of course, would also help.

So, where does NASA stand in all this? As it turns out, NASA’s amazing views of the Earth at night helped to create an unsurpassed view of the light pollution engulfing the planet. The Earth Observatory System and Visible Infrared Imaging Radiometer Suite satellites have given people a new perspective of light pollution and human impact on Earth. After all, NASA has always had an amazing ability to open the eyes of the public with breathtaking pictures from space. NASA’s EOS will only continue to raise awareness and make detailed measurements of the spread of light pollution in the future. For years, NASA has been writing articles and using pictures to inform the public about light pollution and organize more information on the topic. Let’s make sure future generations will be able to stargaze, enjoy a healthy environment, and get a good night’s sleep. A Penny4NASA can help control light pollution.

Where i live is in a place that has and less than 100 stars, I HATE LIGHT POLLUTION, Wish they would do something about it! the people should see the true dark night sky!

Roy McMillan II

They have done something about it..it is called rural America. This charts and “ENHANCED” photos and images on here are a bunch of bunk. I have driven across the U.S. during daytime hours and night as well. Your images of nighttime light pollution are so skewed from truth, it is laughable. Especially how the image of 1997 show all kinds of light pollution from Omaha Nebraska to Reno NV. At night, this part of the country through there is some of the deepest dark night you can find. Billions of stars shining brightly in the night sky. I have seen the big cities and Muchn of what is stated has merit in the laege metro areas, but that is as far as it goes.

Janie Doe

“ENHANCED” true but I’m pretty sure that the International Dark Sky’s movement to control the pollution would have made a significant difference since 1977.

Janie Doe

I’m sorry, Roy McMillan II, I don’t think I read that right. Are you calling PhD carrying scientists who study this for a living liars?